The present invention relates generally to hydraulic lash adjusters for internal combustion engines, and more particularly, to a hydraulic lash adjuster (HLA) which is very compact in size, especially in overall length.
Although the present invention may be utilized in conjunction with hydraulic lash adjusters for use with a number of different types of engine valve gear train, the invention is especially advantageous when used in a valve gear train of the end-pivot rocker arm type, and will be described in connection therewith. When an HLA is used in an end-pivot rocker arm type of valve gear train, the HLA is stationary and is disposed in a bore formed in the engine cylinder head.
A conventional HLA of the type to which the invention relates includes an output plunger assembly engaging the rocker arm (in the case of an overhead cam engine) with the output plunger assembly typically being of either a one piece or a two piece construction. The plunger assembly includes a ball plunger element which engages a socket formed in the rocker arm, and a leakdown plunger element which defines a check valve seat and further defines a leakdown land, the leakdown plunger element being precisely fit within a bore of the body to provide a closely controlled fluid leakdown path during normal operation.
The above-described plunger assembly results in an overall HLA structure which is relatively long, such that it can be difficult to allocate sufficient space within the cylinder head to locate the HLA. The above-described problem is particularly acute in some of the new, compact, multi-valve engines. The length of conventional, prior art hydraulic lash adjusters can also cause constraints on other aspects of the design of the engine, such as valve location, valve angle, the location and orientation of the spark plug, and the location of oil galleries, coolant passages and valve ports.